1. Summary of the Invention
The present invention relates to discharge chutes on mixing vehicles and, more particularly, to apparatus and methods securing a discharge chute at a desired position about its range of motion.
2. Description of the Related Art
Vehicles designed to mix and transport concrete typically include mixing drums in which the liquid concrete is held during transportation. The mixing drums normally have a capacity of between seven and ten cubic yards of concrete. This volume of concrete typically weighs between 28,000 lbs and 40,000 lbs. The mixing drums typically rotate on the mixing vehicle to agitate the mass of liquid concrete and to prevent it from setting during transport.
The mixing drums are typically set at an angle on the mixing vehicle which places the discharge opening of the mixing drum above the level of a full load of concrete. When the concrete is to be discharged, rotation of the drum is typically reversed which directs the liquid concrete outwardly through a discharge opening. This discharge opening is typically positioned at the front or rear of the vehicle. The discharged concrete is received and guided to the desired location by a pivoting discharge chute. The discharge chute is typically mounted below the discharge opening. The discharge chute is typically configured to pivotally rotate about a vertical axis on the vehicle. Accordingly, the chute may direct concrete to either side or to the front/rear of the mixing vehicle depending upon the particular configuration of the vehicle. Extensions of the chute may be employed to direct concrete to locations more remote from the vehicle.
At 4,000 pounds per cubic yard, the liquid concrete can produce substantial forces as it is directed by and moves along the discharge chute. When disposed along a long extension, the dynamic mass of concrete can produce significant torque at the connection of the discharge chute to the vehicle. Given the pivoting nature of a typical discharge chute, the forces on the discharge chute can produce movement which is difficult to manually control and may result in unwanted movement of the discharge chute. This movement of the discharge chute can result in the misdirection of the liquid concrete which wastes both the concrete and the man-hours needed for cleanup. In addition, a freely swinging chute can present a significant safety hazard for those working around the discharge chute. Accordingly, various devices and alternative configurations have been employed for controlling and/or locking discharge chutes in a desired position.
Some prior devices for securing the position of a chute include manual operable clamp assemblies mounted to a pivoted chute brace. These clamp assemblies typically consist of a threaded shaft at one end of an upright brace bearing shaft. A wheel is typically threadably engaged to a shaft and can be selectively tightened against the shaft journal to clamp a brace tightly to a vehicle 100 frame. This brace-type brake is partially serviceable for standard length chutes. However, the locking mechanism can vibrate loose and allow the chute to pivot freely.
U.S. Pat. No. 3,279,766 to F. V. Mendoza discloses a transit concrete mixer with particular reference to a brake mechanism. The mechanism disclosed enables selective angular positioning of a concrete chute. The brake components used are of typical automotive drum brake design with axially oriented shoes and brake surfaces. A hydraulic brake cylinder is utilized for actuation of the brake shoes selectively bringing them radially against a brake drum.
The problem of braking a discharge chute at the pivotal mount for the discharge chute is also recognized to a limited degree in the U.S. Patent to Hansen et al, U.S. Pat. No. 3,334,872. Hansen et al discloses a double ended piston hydraulic cylinder that controls pivotal movement of a discharge chute at the chute's mounting point on the concrete mixing truck. The cylinder operates to pivot the discharge chute about its axis and also acts as a positive brake.
The hydraulic cylinder requires use of an expensive and complex hydraulic system that is not typically supplied as standard equipment on concrete mixing trucks. Hydraulic cylinders wear quickly when exposed to concrete with its naturally abrasive component. Maintenance and repair therefore become frequent. Furthermore, use of a hydraulic cylinder could be considered “overkill”, since the primary need is not for powered movement of the chute. The discharge chute is usually empty when moved from one position to another. The primary need is for holding the discharge chute stationary after being angularly positioned, when it is full of heavy concrete.
U.S. Pat. No. 3,410,538 to M. L. Potter discloses a positive locking apparatus for positioning a discharge chute at any of several pre-selected angular positions. Potter's arrangement uses a positive detent type lock between the chute frame and a pressure plate pivoted with the chute. A pin is used to interconnect the stationary frame with the pivoted pressure plate by insertion within one of several angularly spaced apertures provided in the movable pressure plate.
The Potter device and other known “detent” type chute locking mechanisms do allow positive positioning of the discharge chute at the pivot point between the discharge chute and stationary frame but do not enable infinite angular adjustment for precise pouring. Further, such mechanisms will not effectively operate to stop a moving discharge chute without causing possible damage to the lockout mechanism. Difficulty is also experienced in removing and placing the lock pin when the discharge chute is loaded.